In a wireless radio access network such as an evolved universal mobile telecommunications system (UMTS) terrestrial radio access network (E-UTRAN), channel quality feedback techniques may be implemented in order to enable evolved node Bs (eNBs) to use suitable modulation and coding schemes (MCSs) when sending messages to user equipment (UEs). According to some such techniques, UEs may periodically and/or aperiodically transmit channel quality indicator (CQI) indices to their serving eNBs. Each CQI index may indicate an MCS that its UE expects to be suitable for use in prospective transmission of a message from an eNB to that UE during a particular subframe.
In some cases, each transmitted message may be transmitted as one or more resource elements (REs) within one or more resource blocks, and the MCS that is actually most suitable for transmitting a particular message may depend on the structures the resource blocks that contain it. Since the UEs cannot know the actual structures of such resource blocks until after they are received, the UEs may define channel state information (CSI) reference resources based on which to select CQI indices. Each CSI reference resource may comprise a generic expected structure for resource blocks via which its associated UE may expect to receive a prospective message during a particular subframe. Once it defines a CSI reference resource for a given subframe, a UE may select a CQI index for that subframe based on the CSI reference resource.
In some wireless radio access networks, the use of particular features may affect the structures of the resource blocks that carry messages to UEs. For example, when an enhanced physical downlink control channel (EPDCCH) is implemented within a physical downlink shared channel (PDSCH) of a E-UTRAN, some REs within PDSCH resource blocks may be allocated to the EPDCCH. In another example, for any particular PDSCH resource block, the number of REs that contain cell-specific reference signals (CRSs) may depend on a number of CRS antenna ports that are configured for the eNB transmitting that PDSCH resource block. In order to enable proper MCS selection, it may be desirable to account for such effects in conjunction with CQI index reporting and/or interpretation, either by incorporating them into the definition of the CSI reference resource on the UE side or by compensating for them on the eNB side.